Chemistry

Thyroglobulin assay in neck cyst is useful to confirm metastatic papillary thyroid carcinoma, when the cyst fluid is too thin to be recognized as thin colloid on Diff-Quik stain (Fig. 14.8). In addition, parathyroid hormone assay is essential in the initial diagnosis of parathyroid cyst (Fig. 13.23).

Immunohistochemistry

Immunostains work best on cell block, but also work very well on Ultrafast Papanicolaou-stained smears due to the presence of formalin in the alcohol-based fixative and the clean background from hemolysis of aspirated blood., The majority of immunostains illustrated throughout this book were done directly on Ultrafast Papanicolaou-stained smears without destaining. Unlike deep-seated FNAs in the hospital setting, immunostains in this series were performed on direct smears primarily because the sample obtained from 27-gauge needles without suction was adequate for making smears but insufficient for making cell blocks.

A positive calcitonin immunostain is essential, prior to total thyroidectomy for medullary carcinoma. If calcitonin immunostain is negative or equivocal, the author will downgrade the diagnosis and report “atypical, cannot exclude” or “suspicious for” medullary carcinoma, so that frozen section will be performed. TTF-1 immunostain is useful in thyroid origin of poorly differentiated carcinoma (Fig. 10.5) and PAX8 useful in thyroid origin of anaplastic carcinoma (Figs. 11.5 and 11.10).

CK19 immunostain is useful to confirm follicular variant of papillary carcinoma. The author encountered an extremely scanty cellular FNA from a calcified nodule. CK19 positivity on the approximately 20 grape-like clear nuclei added immunohistochemical evidence of follicular variant of papillary carcinoma (Fig. 16.1).

Other useful immunomarkers for papillary carcinoma include HBME-1 and galactin-3 (Fig. 16.2). In a study to evaluate the usefulness of four immunomarkers in the histological diagnosis of encapsulated follicular tumors with questionable nuclear features of papillary carcinoma, Scognamiglio et al. reported that all four markers showed higher expression in encapsulated follicular variant of papillary carcinoma than follicular adenoma. HBME-1 was the most specific (96%), whereas CK19 was the most sensitive (96%). 100% specificity was seen with coexpression of HBME-1 and CK19. Galactin-3 and CITED1, less useful individually, were helpful in selective cases.